Torque sensor for an electric bicycle

ABSTRACT

An electric bicycle having an electric motor mounted to a frame of the bicycle and which includes a motor output shaft defining an output end engaging a drive chain of the bicycles drive train to transmit the drive of the electric motor thereto. A torque sensor includes a base mounted in fixed relation to the frame and/or the electric motor. The torque sensor has a flexible arm extending from the base and a sensing member mounted to an extremity of the flexible arm that is displaceable relative to the base. The sensing member engages the drive chain along a segment thereof and is displaceable thereby. The segment of the drive chain extends from the output end of the motor output shaft to the pedal crank of the drive train.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from U.S. Patent Application No.62/461, 284 filed Feb. 21, 2017, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to bicycles, and moreparticularly, to electric bicycles.

BACKGROUND

Bicycles driven in whole or in part by assisted power are known in theart. The assisted power complements the driving force generated by therider of the bicycle, and may replace it altogether. The assisted powercan be provided by an internal-combustion or electric motor integratedwith the bicycle.

Regardless of the source of the assisted power, it is useful to monitorthe torque being applied to the chain of the bicycle. Depending on themeasured torque, the assisted power can increase or decrease its outputof torque to match the needs of the rider. Conventional devices formonitoring torque may be too large to be used in compact electricmotors, may be exposed to the elements and thus susceptible to damage,and/or may capture torque values too slowly to be effective incomplementing the driving force of the rider.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided an electric bicycle, comprising: a frame to which a front wheeland a rear wheel are rotatably mounted and having a bottom bracketshell; a drive train having a rotatable pedal crank mounted about thebottom bracket shell, the pedal crank being rotated by a pedalingactuation, and a drive chain extending between and engaging the pedalcrank and a rear sprocket of the rear wheel to transmit the pedalingactuation to the rear wheel; an electric motor mounted to the frame andhaving a motor output shaft, the motor output shaft defining an outputend engaging the drive chain to transmit the drive of the electric motorthereto; and a torque sensor having a base mounted in fixed relation tothe frame and/or the electric motor, the torque sensor having a flexiblearm extending from the base and a sensing member mounted to an extremityof the flexible arm, the extremity being displaceable relative to thebase, the sensing member engaging the drive chain along a segmentthereof and being displaceable thereby, the segment of the drive chainextending from the output end of the motor output shaft to the pedalcrank of the drive train.

There is also provided, in accordance with another aspect of the presentinvention, an electric propulsion system for a bicycle mountable to aframe of the bicycle, the electric propulsion system comprising: ahousing mountable to the frame; an electric motor disposed within thehousing and having a motor output shaft, the motor output shaft definingan output end disposed within the housing and engageable with a drivechain of the bicycle to transmit the drive of the electric motorthereto; and a torque sensor having a base mounted in fixed relation tothe frame and/or the electric motor, the torque sensor having a flexiblearm extending from the base and a sensing member mounted to an extremityof the flexible arm, the extremity being displaceable relative to thebase, the sensing member being engageable with the drive chain along asegment thereof and being displaceable thereby, the segment of the drivechain extending from the output end of the motor output shaft to a pedalcrank of the bicycle.

In the electric propulsion system described herein, the torque sensormay be disposed within the housing.

The electric propulsion system described herein may further comprise amagnet mounted to the arm between opposed extremities thereof, and aHall effect sensor mounted to the housing and spaced from the magnet.

There is further provided, in accordance with another aspect of thepresent invention, a torque sensor mountable to a bicycle having a frameand an electric motor, the torque sensor comprising: a flexible arm anda sensing member mounted to an extremity of the arm, the sensing memberbeing engageable with a drive chain of the bicycle along a segmentthereof and being displaceable by the drive chain, the segment of thedrive chain extending from an output of the electric motor to a pedalcrank of the bicycle.

In the torque sensor described herein, a first extremity of the flexiblearm may include a mounting bracket and the sensing member is disposed ata second extremity of the arm.

In the torque sensor described herein, the sensing member may include arotatable gear disposed at the second extremity of the arm andengageable with the drive chain.

In the torque sensor described herein, the flexible arm may be curvedbetween the first and second extremities, a curvature length beingdefined between the first and second extremities along a curvature ofthe curved flexible arm, a straight line being defined between the firstand second extremities and having a straight line length, the curvaturelength being greater than the straight line length.

In the torque sensor described herein, the flexible arm may have atwisted portion between the first and second extremities thereof, thetwisted portion having a first segment linked to the sensing member, asecond segment linked to the mounting bracket, and a third segmentbetween the first and second segments, the first and second segmentsbeing spaced apart in overlapping arrangement.

In the torque sensor described herein, the flexible arm may have atwisted portion between the first and the second extremities thereof,the twisted portion having a first segment linked to the sensing member,a second segment linked to the mounting bracket, and a third segmentbetween the first and second segments, each of the first, second, andthird segments being curved along their length, and the twisted portionbeing sinuous along an extent thereof.

The torque sensor described herein may further comprise a magnet mountedto the arm between opposed extremities thereof.

In accordance with another aspect of the present, there is also provideda method for converting a non-electric bicycle into an electric bicycle,the method comprising: providing an electric motor having a motor outputshaft defining an output end, and providing a torque sensor having aflexible arm and a rotatable sensing member mounted to an extremity ofthe arm; mounting the electric motor to a frame of the non-electricbicycle; and extending a drive chain at least between a pedal crank ofthe non-electric bicycle, the output end of the motor output shaft, andthe sensing member of the torque arm, the sensing member engaging thedrive chain between the output end and the pedal crank.

In the electric bicycle described herein, the flexible arm of the torquesensor may be curved between the base and the extremity, a curvaturelength being defined between the base and the extremity along acurvature of the curved flexible arm, a straight line being definedbetween the base and extremity and having a straight line length, thecurvature length being greater than the straight line length.

In the electric bicycle described herein, the flexible arm of the torquesensor may have a twisted portion between the base and the extremitythereof, the twisted portion having a first segment linked to thesensing member, a second segment linked to the base, and a third segmentbetween the first and second segments, the first and second segmentsbeing spaced apart in overlapping arrangement.

In the electric bicycle described herein, each of the first, second, andthird segments may be curved along their respective lengths, and thetwisted portion being sinuous along an extent thereof.

In the electric propulsion system described herein, the flexible arm ofthe torque sensor may be curved between the base and the extremity, acurvature length being defined between the base and the extremity alonga curvature of the curved flexible arm, a straight line being definedbetween the base and extremity and having a straight line length, thecurvature length being greater than the straight line length.

In the electric propulsion system described herein, the flexible arm ofthe torque sensor may have a twisted portion between the base and theextremity thereof, the twisted portion having a first segment linked tothe sensing member, a second segment linked to the base, and a thirdsegment between the first and second segments, the first and secondsegments being spaced apart in overlapping arrangement.

In the electric propulsion system described herein, each of the first,second, and third segments may be curved along their respective lengths,and the twisted portion being sinuous along an extent thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1A is a schematic side elevation view of an electric bicycle havingan electric propulsion system, according to an embodiment of the presentdisclosure;

FIG. 1B is an enlarged view of the electric propulsion system of FIG. 1Ashowing a torque sensor;

FIG. 2 is a perspective view of the electric propulsion system andtorque sensor of FIG. 1B;

FIG. 3A is a perspective view of the torque sensor of FIG. 1B;

FIG. 3B is another perspective view of the torque sensor of FIG. 1B;

FIG. 3C is a side elevation view of the torque sensor of FIG. 1B; and

FIG. 4 is a perspective view of a torque sensor according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A and 1B illustrate an electric bicycle 10. By “electric”, it isunderstood that the bicycle 10 can be partially or entirely driven by amotive force supplied by an electric motor, or which can be whollydriven only by pedal power when desired. The motive force can thereforealso be disengaged so that the bicycle 10 can be driven entirely by thepedalling actuation force generated by the rider. The bicycle 10 cantake many different configurations, and have a different frame andconfiguration of components than that shown in the figures, providedthat it remains at least partially electrically-driven by an electricpropulsion system as will be described below. The electric bicycle 10may be either configured to be a road or city bike, or a mountain bike.The bicycle 10 has a frame 20, a drive train 40, and an electricpropulsion system 60.

The frame 20 forms the corpus of the bicycle 10 and provides structurethereto so that it can be used by a rider. For example, the frame 20shown in FIG. 1A may be either a “hardtail” bicycle 10 (i.e. one havingno suspension) or a suspended (or “fully suspended”) bicycle (i.e. onehaving a rear suspension). Many other types of frames 20 are also withinthe scope of the present disclosure, including for example mountainbicycles or street bicycles having a rear suspension. For example, inaddition to the multi-body construction of the frame 20 of FIGS. 1A and1B, the frame 20 can be of a unibody construction if so desired.Irrespective of its shape or configuration, the frame 20 of the presentdisclosure has a front frame portion 21, a rear frame portion 23, and abottom bracket shell 25, all of which are now described in greaterdetail.

The front frame portion 21 forms the front of the frame 20 and includesthe front wheel fork which is attached at its most forward end to thefront wheel 22 of the bicycle 10, which rotates about a wheel axis. Thefront frame portion 21 of the main frame includes at least a down tube26, and can also include a top tube, a seat tube, a head tube, afront-wheel suspension, etc. Indeed, the front frame portion 21 can havemany other components, depending on the configuration of the bicycle 10and its intended use, among other possible factors.

The rear frame portion 23 forms the rear of the frame 20 and is attachedat its rearmost end to the rear wheel 24, which also rotates about arear wheel axis. The rear frame portion 23 has stays 27, such as seatand chain stays, which link the rear wheel 24 to the front frame portion21. As with the front frame portion 21, the rear frame portion 23 mayinclude other bicycle components including, but not limited to, arear-wheel suspension, a rear wheel sprocket, a rear wheel hub, aderailleur, etc.

The front and rear frame portions 21, 23 meet generally in the vicinityof the seat tube 29 of the frame 20, and define junctions. One suchjunction may be formed where the down tube 26 and the chain stays 27meet, and defines a bottom bracket shell 25. The bottom bracket shell 25may be located elsewhere on the frame 20 at a bottom end thereof. Thebottom bracket shell 25 (or simply “bottom bracket 25”) is essentially ahollow tubular portion extending between the left and right sides of thebicycle 10 along a center axis. The bottom bracket 25 receives therein acrank shaft as will be seen.

Still referring to FIGS. 1A and 1B, the drive train 40 is adapted toreceive a pedalling actuation, or input of force, from the rider of thebicycle 10. The drive train 40 can be coupled or connected to theelectric propulsion system 60, as required, so that the electricpropulsion system 60 can complement or replace the force applied by theuser. Alternatively, the drive train 40 can be decoupled or disconnectedfrom the electric propulsion system 60 so that the rider can supply allthe force required to propel the bicycle 10. The drive train 40 includesa crank shaft 41, a pedal crank 43 (ex: one or more chain rings), and adrive chain 45.

The crank shaft 41 is rotatably mounted within the bottom bracket 25 andextends transversely therethrough between the left and right sides ofthe bicycle 10. The crank shaft 41 rotates about a central crank shaftaxis, which is coincident with the axis of the bottom bracket 25 whenthe crank shaft 41 is disposed within the bottom bracket 25. The crankshaft 41 is therefore supported by suitable bearings so that it canrotate with respect to the stationary bottom bracket 25 about the crankshaft axis.

The pedal crank 43 (or simply “crank 43”) can be any rotatable gear orgears which engage the drive chain 45. In so doing, the crank 43 is ableto transfer the rotary force generated by the rider to the rear wheel 24via the drive chain 45. The crank 43 is disposed on either the left orright side of the bicycle 10, and is mounted to the crank shaft 41. Afreewheel clutch may also be provided between the crank 43 and the crankshaft 41. Since the crank 43 is a gear, it can have any suitable size orshape to achieve a desired functionality. For example, the number ofteeth or sprockets on the crank 43 can vary depending on the drive chain45 being used, and the retail cost of the bicycle 10, to name but a fewfactors. Optionally, the number of teeth can be thirty-eight orforty-two, and cranks 43 having a different number of teeth are alsowithin the scope of the present disclosure.

Crank arms 44 are mounted to the crank 43 in fixed engagement. The crankarms 44 transmit the pedalling force generated by the user to the drivetrain 40. The free ends of the crank arms 44 typically have pedalsagainst which the feet of the rider apply force. The application of thisforce to the pedals by the rider creates a pedalling actuation, which isa rotation of the pedals and the crank arms 44 about the crank shaftaxis, which in turn rotates the crank shaft 41 and the crank 43. Thepedals and crank arms 44 may also be rotated in a direction which doesnot result in forward propulsion of the bicycle 10, either freely or inorder to provide a braking action. The crank arms 44 are mounted to bothextremities of the crank shaft 41 on the left and right sides of thebicycle 10.

Still referring to FIGS. 1A and 1B, the drive chain 45 forms themechanical linkage between the drive train 40, specifically the crank43, and the rear wheel 24, specifically its rear wheel sprocket 28mounted to the rear wheel 24 concentrically about its wheel axis. Therear sprocket 28 can include more than one sprocket 28, and can be acassette or include a freewheel. In the depicted embodiment, the drivechain 45 is located on the same side of the bicycle 10 as the crank 43.Such a positioning of the drive chain 45 and crank 43 advantageouslyallows for a derailleur to be used with the rear sprocket 28, if sodesired. It can thus be appreciated that the drive chain 45 facilitatesthe transfer of the pedalling actuation from the crank 43 to the rearwheel 24.

The bicycle 10 also has an electric propulsion system 60, thereby makingthe bicycle 10 an electric bicycle 10 (or electrically-driven bicycle10). The electric propulsion system 60 (or simply “propulsion system60”) assists the rider of the bicycle 10 by providing an additional andcomplementary motive force to help the rider propel the bicycle 10forward. The propulsion system 60 can be the sole motive forcepropelling the bicycle 10 forward, or a portion thereof. The bicycle 10may therefore constitute an electrically-assisted bicycle.Alternatively, the propulsion system 60 can be decoupled so that itprovides no motive force at all, whereby the bicycle 10 operates likeany standard non-motorized bicycle.

As its name suggests, the propulsion system 60 is an electrical system,and thus generates its motive force, or “drive”, electrically using anysuitable technique. The drive provides a rotational output of power fromthe propulsion system 60, and specifically from its electric motor. Thedrive can be applied as a permanent force, or selectively by the rider.The propulsion system 60 can thus be powered by any suitable technique,such as electrochemical cells or an electrical-energy storage device.Optionally, the propulsion system 60 can employ a regenerative breakingto recharge its power source. In the depicted embodiment, the driveproduced by the propulsion system 60 is applied to the rear wheel 24 ofthe bicycle 10. The present propulsion system 60 is relatively compactand lightweight, such that it can be secured to the frame 20. Typically,the propulsion system 60 is mounted to the down tube 26 and/or the seattube 29 of the front frame portion 21 of the bicycle frame 20, howeverit can also be mounted elsewhere on the frame 20.

The propulsion system 60 disclosed herein is separate from the bottombracket shell 25 of the frame 20. More particularly, the propulsionsystem 60 is mounted to a part of the frame 20 which is at a distancefrom, and thus separate from, the bottom bracket shell 25. Thepropulsion system 60 can therefore be mounted to non-electric bicyclesso as to provide a motive force that compliments the force provided bythe drive train 40, without having to disrupt or modify the existinggeometry and ergonomics of the originally non-electric bicycle. Thepropulsion system 60 can therefore be used to retro-fit or convert anon-electric bicycle into an electric bicycle 10, as will be explainedin greater detail below. This contrasts with some conventional electricpropulsion systems, which must be mounted through the bottom bracket ofthe frame, thereby requiring a purpose-built frame configuration andthus often negatively affecting the geometry of the bicycle and the feelof the bicycle to which the user has become accustomed.

Still referring to FIGS. 1A and 1B, the propulsion system 60 includesgenerally an electric motor 30 for generating the drive which assiststhe rider and provides motive power to the bicycle 10. The electricmotor 30 can thus be any suitable electric machine which convertselectrical energy into mechanical motion. The electric motor 30 maytherefore have circuitry or electronics cards which govern the power itapplies, and its operation. Similarly, the electronic motor 30 has anysuitable controllers or processors to process the information providedto the electric motor 30 and to govern its operation.

The electric motor 30 can be contained within a suitable housing 34 orcasing which shelters the electric motor 30 and other components of thepropulsion system 60 from debris, moisture, and the elements. Thehousing 34 can have a support bracket 35 which secures the housing 34 inplace to the frame 20. The support bracket 35 can secure the housing 34(and thus the motor 30) to the frame 20 at a distance from the bottombracket shell 25. The support bracket 35 can be removed in order topermit access to the electric motor 30. FIG. 1B shows an interior of theelectric motor 30 after the support bracket 35 and part of the housing34 have been removed. The electric motor 30, or the housing 34 in whichit is contained, are secured to the bicycle frame 20, generally to thedown tube 26 and/or the seat tube 29.

Still referring to FIG. 1B, the electrical output of the electric motor30 generates mechanical motion. The electric motor 30 has a rotor whichrotates within a stator inside of the housing 34. A motor output shaft31 rotates with the rotor, thereby providing useful mechanical motion.The motor output shaft 31 (or simply “motor shaft 31”) rotates about amotor shaft axis, which is fixed in position along with the motor shaft31 in the housing 34 of the electric motor 30 The motor shaft axis formsthe centerline of the motor shaft 31 and extends along its length. Themotor shaft 31 outputs the rotational mechanical motion generated by theelectric motor 30, and thus has an output end 33 located within thehousing 34. In the depicted embodiment, the output end 33 is on the sameside of the bicycle 10 as the crank 43. This configuration of the outputend 33 allows the output end 33 to engage the drive chain 45 andtransmit the drive of the electric motor 30 thereto. FIG. 1B shows theoutput end 33 having an output sprocket 36 engaged with the drive chain45. Many other configurations of the output end 33 are within the scopeof the present disclosure. The speed of the motor output shaft 31, andthus of the output end 33, can vary. One possible range of rotationalspeeds at the output of the motor is between about zero and about 1, 200RPM, and other rotational speeds and ranges of rotational speeds arewithin the scope of the present disclosure. It can thus be appreciatedthat the electrical drive generated by the electric motor 30 isoutputted as a mechanical drive via the output end 33 to the drive chain45, which provides motive power to the bicycle 10.

Still referring to FIG. 1B, the bicycle 10 includes a torque sensor 50.The torque sensor 50 includes a sensor, meter, or transducer formeasuring and/or recording the torque on a rotating component, and willnow be described in further detail.

In the depicted embodiment, the torque sensor 50 measures the torqueapplied to the drive chain 45. The torque sensor 50 is thereforedisposed in fixed relation to the frame and/or the electric motor, so asto record torque values from the displacement of the drive chain 45resulting from the drive supplied by the electric motor 30 and/or thecrank 43. In the depicted embodiment, the fixed disposition of thetorque sensor 50 is obtained by mounting the torque sensor 50 to thehousing 34 of the electric motor 30. In the depicted embodiment, thetorque sensor 50 is disposed within the housing 34, thereby protectingthe torque sensor 50 from debris, moisture, and the elements. In analternate embodiment, the torque sensor 50 is mounted to a portion ofthe frame 20 of the bicycle 10.

As seen in FIGS. 2 to 3C, the torque sensor 50 includes a base portionfixedly mounted to the frame and/or the electric motor, and a flexiblearm 52 extending from the base portion. In the depicted embodiment, theflexible arm 52 is fixedly mounted to the housing 34 and/or the frame ata first extremity 54 of the arm 52 (i.e. forming the base portion) thatdoes not move relative to the housing 34 and/or the frame to which it isfixed. A second, remote, extremity 56 of the arm 52 is not attached toanother structure, and is therefore free to be displaced by the drivechain 45 relative to the fixed base portion of the torque sensor 50, asexplained in greater detail below. The displacement of the free secondextremity 56 of the arm 52 relative to the immobile first extremity 54causes flexion of the arm 52. In the depicted embodiment, the flexion ofthe arm 52 is elastic under normal operating conditions, such that thearm 52 will revert to its original form and position after being flexed.The resiliency of the arm 52 can be obtained from the material fromwhich it is made, the size of its elements, or its configuration, asdiscussed in greater detail below.

In the depicted embodiment, the flexible arm 52 is curved along itslength between the first and second extremities 54, 56. A length of thecurved flexible arm 52 is defined between the first and secondextremities 54, 56 along a curvature of the arm 52. The length ofcurvature of the arm 52 is greater than the length of a straight lineextending directly between the first and second extremities 54, 56.

The torque sensor 50 also has a sensing member 58 mounted to the freesecond extremity 56 of the arm 52. The sensing member 58 engages thedrive chain 45 and is displaced by movement of the drive chain 45. Inthe depicted embodiment, the sensing member 58 is biased toward thedrive chain 45 to maintain engagement therewith. The flexible arm 52therefore applies a torque to the drive chain 45 about the base portion.In at least the depicted embodiment, the flexible arm 52 is therefore atorque arm 52. The displacement of the sensing member 58 causes theflexion of the arm 52, thereby permitting the torque on the drive chain45 to be determined.

Referring to FIG. 2, the sensing member 58 engages a segment 46 of thedrive chain 45. The segment 46 of the drive chain 45 extends from theoutput end 33 of the motor output shaft 31 to the pedal crank 43 of thedrive train 40. Stated differently, the sensing member 58 engages thedrive chain 45 at a point thereon which, in a direction of travel D ofthe drive chain 45, is “downstream” (i.e. along the direction of travelD) of the output end 33 of the electric motor, and “upstream” (i.e.against the direction of travel D) of the pedal crank 43. The sensingmember 58 therefore engages the drive chain 45 between the two primarysources of torque acting on the drive chain 45, i.e. between the outputof torque provided by the electric motor 30 and the output of torqueprovided by the rider to the crank 43.

When the bicycle 10 is in use, the output of torque from the output end33 of the motor and from the pedal crank 43 will vary. The tension ofthe segment 46 of the drive chain 45 will therefore also vary. Thechange in tension along the segment 46 will cause the sensing member 58to be displaced. For example, in the embodiment where the sensing member58 is biased toward the drive chain 45 to maintain engagement therewith,an increase in torque will cause the segment 46 to become more taughtand thus “straighten out”, and thereby cause the sensing member 58 to bedisplaced in direction T1. Similarly, a decrease in torque will createslack along the segment 46, and thereby cause the biased sensing member58 to be displaced in direction T2. The displacement of the sensingmember 58 will cause the arm 52 to resiliently flex, thereby allowing atorque measurement to be taken, as described in greater detail below.

It is understood that positioning the sensing member 58 along thesegment 46 allows the torque sensor 50 to capture the tension in thedrive chain 45 caused by the torque applied by the user at the crank 43,and by the torque provided by the electric motor 30. The ability tomeasure torque at this location provides for quick readings of torque,and thus faster reaction times for the electric motor 30 output. Stateddifferently, since the torque sensor 50 allows torque to be measuredalong the segment 46 of the drive chain 45 that is typically the mosttaught and right after it has been generated by the electric motor 30,the electric motor 30 is able to provide close to real-time torqueadjustments to assist the rider. This compares favourably withconventional devices which measure torque along other parts of the drivechain where there is slack or which are further away from the twoprimary sources of torque. These conventional devices are too slow todetermine the torque requirements of the rider, and may thus cause theassisted power to provide torque assist before or after it is required.Furthermore, by measuring torque directly from the drive chain 45, thetorque sensor 50 avoids having to determine torque from the rotation ofcomponents such as the crank shaft 41 and the motor output shaft 31.

The information or signal generated by the torque sensor 50 iscommunicated to the electric motor 30. More particularly, the signalgenerated by the torque sensor 50 may be processed to provide a suitablemotor input signal that is communicated to the controller of theelectric motor 30. The controller then applies the appropriate logic tothe received motor input signal to govern the output of the electricmotor 30 so as to increase, decrease, or leave unchanged its torqueoutput. The signal generated and communicated by the torque sensor 50can be an analog signal or a digital signal.

Referring still to FIG. 2, in the depicted embodiment, the sensingmember 58 includes a rotatable element. More particularly, the sensingmember 58 includes a rotatable jockey wheel or gear 51 at the secondextremity 56 of the arm 52. The teeth of the gear 51 engage the links ofthe drive chain 45 such that displacement of the drive chain 45 alongits direction of travel D causes the gear 51 to rotate about its axis.In alternate embodiments, the sensing member 58 includes a non-rotatingelement, such as a guide rail or a slot in the second extremity 56 ofthe arm 52, against which the segment 46 of the drive chain 45 isengaged. The arm 52 also includes a mounting bracket 53 at the firstextremity 54 thereof. The mounting bracket 53 mounts the arm 52 to astructure of the bicycle 10. In the depicted embodiment, the mountingbracket 53 fixedly mounts the arm 52 to the housing 34 of the electricmotor 30.

In the depicted embodiment, the torque sensor 50 has a sensor assembly55 for measuring the torque on the drive chain 45. The sensor assembly55 includes a magnet 55A mounted to the arm 52 between the first andsecond extremities 54, 56 thereof. In the depicted embodiment, themagnet 55A is mounted within a grooved magnet housing 55B formed in thearm 52. The sensor assembly 55 also includes a Hall effect sensor 55Cmounted to the housing 34 of the electric motor 30 and spaced from themagnet 55A. Similarly to the magnet 55A, the Hall effect sensor 55C ishoused within a sensor housing 55D. The sensor housing 55D in thedepicted embodiment is part of the housing 34 of the electric motor 30.The sensor housing 55D is therefore stationary with respect to themagnet 55A, and the magnet 55A displaces with the arm 52 when the arm 52undergoes flexion. The Hall effect sensor 55C outputs a voltage inresponse to the proximity of the magnet 55A thereto. When the engagementof the sensing member 58 with the drive chain 45 causes the arm 52 todisplace under flexion, as explained above, the magnet 55A is displacedwith the flexible arm 52 towards or away from the Hall effect sensor55C. This varies the voltage output of Hall effect sensor 55C, therebyenabling the torque on the drive chain 45 to be determined as a functionof the voltage output of the Hall effect sensor 55C.

Other techniques for determining the flexion or strain on the arm 52 arealso within the scope of the present disclosure. For example, in onealternative embodiment, the arm 52 has a strain gauge mounted thereon.When force is applied to the arm 52 by the drive chain 45, the armunderdoes strain. The strain gauge is a type of sensor whose resistancevaries with strain experienced by the arm 52. This change in electricalresistance is measurable and can be processed to determine the torque onthe drive chain 45. In another alternative embodiment, a metal componentis mounted to the arm 52 to be displaced therewith, and an inductionsensor is part of the housing 34 or frame 20. The induction sensor istherefore stationary with respect to the metal component. The inductionsensor measures the displacement of the metal component. The signal fromthe induction sensor is processed to determine the torque acting on thedrive chain 45.

From the above description of the techniques for determining the flexionor strain on the arm 52, it will be appreciated that many “contact-less”techniques are within the scope of the present disclosure. Eachcontact-less technique allows the arm 52 to displace freely, and for itsdisplacement to be measured without having to contact the arm 52.

FIGS. 3A to 3C are views of the torque sensor 50 in isolation. In thedepicted embodiment, the flexible arm 52 has a twisted portion 57. Thetwisted portion 57 is a portion of the arm 52 between its first andsecond extremities 54, 56 that is bent, curved, or otherwise distorted.The twisted portion 57 increases the overall length of the flexible arm52 while allowing it to occupy a relatively overall space envelope (i.e.a relative small total volume). The twisted portion 57 thereforefacilitates placing the torque sensor 50 within the relatively compacthousing 34 of the electric motor 30.

In the depicted embodiment, the twisted portion 57 has a first segment57A, a second segment 57B, and a third segment 57B. The first segment57A is structurally linked to the sensing member 58 and extends to thesecond extremity 56. The second segment 57B is structurally linked tothe mounting bracket 53 and extends to the first extremity 54. The thirdsegment 57C extends between and links the first and second segments 57A,57B. Distal ends 57D of the third segment 57C are curved and form curvedlinkages with the first and second segments 57A, 57B. In the depictedembodiment, the first and third segments 57A, 570 are also curved alongtheir length. The first and second sections 57A, 57B are spaced apartfrom each other in an overlapping arrangement. This overlappingarrangement is better appreciated in FIG. 2, which shows the firstsegment 57A lying over and in front of the second segment 57B. It canthus be appreciated that this “coiled” configuration of the arm 52 helpsthe arm 52 undergo resilient flexion. The overlapping segments 57A, 57Bof the twisted portion 57 help to spread flexion of the arm 52 overlonger distances, which may ease the overall strain experienced by thearm 52 when in flexion. This reduced strain may also prevent plasticdeformation of the arm 52.

This configuration of the arm 52 allows it to resiliently flex in atleast two directions in response to force applied to the sensing member58 via the drive chain 45. The first direction F1 of resilientdeflection is shown in FIGS. 3A and 3B, and is similar to directions T1and T2 described above. The second direction F2 of resilient deflectionis shown in FIGS. 3A and 3C, and is transverse to the first directionF1. Resilient deflection of the arm 52 along the second direction F2allows the arm 52 to accommodate and adapt to unpredictable movements ofthe drive chain 45.

FIG. 4 shows another embodiment of the torque arm 150, with a differentconfiguration of the twisted portion 157. The twisted portion 157 islocated between the first and second extremities 154, 156 of the torquearm 150. In the depicted embodiment, the twisted portion 157 has a firstsegment 157A, a second segment 157B, and a third segment 157B. The firstsegment 157A is structurally linked to the sensing member 58 (whichincludes a gear 51) and extends to the second extremity 156. The secondsegment 157B is structurally linked to the mounting bracket 153 andextends to the first extremity 154. The third segment 157C extendsbetween and links the first and second segments 157A, 157B. In thedepicted embodiment, the first, second, and third segments 157A, 157B,157C are curved along their length. The curved segments 157A, 157B, 157Cgive the twisted portion 157 a sinuous form along its extent. Thiscompact winding configuration of the twisted portion 157 increases theoverall length of the flexible arm 152 while allowing it to occupy arelatively overall space envelope (i.e. a relative small total volume).It can thus be appreciated that this serpentine configuration of the arm152 helps the arm 152 undergo resilient flexion. The sinuous segments157A, 157B, 157B of the twisted portion 157 help to spread flexion ofthe arm 152 over longer distances, which may ease the overall strainexperienced by the arm 152 when in flexion. This reduced strain may alsoprevent plastic deformation of the arm 152.

FIG. 4 also shows the gear 51 of the sensing member 58 engaged with thedrive chain 45 between the output end 33 of the electric motor 30 andthe crank 43. FIG. 4 also shows the sensor assembly 55 with its magnet55A mounted to the arm 152 between the first and second extremities 154,156 thereof. The Hall effect sensor 55C of the sensor assembly 55 ismounted to the housing 34 of the electric motor 30 and spaced from themagnet 55A.

Other embodiments of the twisted portion 57, 157 are also within thescope of the present disclosure. In one such embodiment, the twistedportion has more than three segments. In this embodiment, multipletwisted and overlapping segments extend between and link the first andsecond segments.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, although shown and described herein as being used with abicycle 10, the torque sensor 50 in alternate embodiments is used with avehicle having fewer or more wheels, such as a unicycle, a tricycle, anda quadricycle. Other modifications which fall within the scope of thepresent invention will be apparent to those skilled in the art, in lightof a review of this disclosure, and such modifications are intended tofall within the appended claims.

1. An electric bicycle, comprising: a frame to which a front wheel and arear wheel are rotatably mounted and having a bottom bracket shell; adrive train having a rotatable pedal crank mounted about the bottombracket shell, the pedal crank being rotated by a pedaling actuation,and a drive chain extending between and engaging the pedal crank and arear sprocket of the rear wheel to transmit the pedaling actuation tothe rear wheel; an electric motor mounted to the frame and having amotor output shaft, the motor output shaft defining an output endengaging the drive chain to transmit the drive of the electric motorthereto; and a torque sensor having a base mounted in fixed relation tothe frame and/or the electric motor, the torque sensor having a flexiblearm extending from the base and a sensing member mounted to an extremityof the flexible arm, the extremity being displaceable relative to thebase, the sensing member engaging the drive chain along a segmentthereof and being displaceable thereby, the segment of the drive chainextending from the output end of the motor output shaft to the pedalcrank of the drive train.
 2. The electric bicycle according to claim 1,wherein the flexible arm of the torque sensor is curved between the baseand the extremity, a curvature length being defined between the base andthe extremity along a curvature of the curved flexible arm, a straightline being defined between the base and extremity and having a straightline length, the curvature length being greater than the straight linelength.
 3. The electric bicycle according to claim 1, wherein theflexible arm of the torque sensor has a twisted portion between the baseand the extremity thereof, the twisted portion having a first segmentlinked to the sensing member, a second segment linked to the base, and athird segment between the first and second segments, the first andsecond segments being spaced apart in overlapping arrangement.
 4. Theelectric bicycle according to claim 3, wherein each of the first,second, and third segments are curved along their respective lengths,and the twisted portion being sinuous along an extent thereof.
 5. Theelectric bicycle according to claim 1, wherein the electric motor isdisposed within a housing mounted to the frame, the output end of themotor output shaft being disposed within the housing.
 6. The electricbicycle according to claim 5, wherein the torque sensor is disposedwithin the housing.
 7. The electric bicycle according to claim 1,further comprising a magnet mounted to the flexible arm between opposedextremities thereof, and a Hall effect sensor mounted to the housing andspaced from the magnet.
 8. An electric propulsion system for a bicyclemountable to a frame of the bicycle, the electric propulsion systemcomprising: a housing mountable to the frame; an electric motor disposedwithin the housing and having a motor output shaft, the motor outputshaft defining an output end disposed within the housing and engageablewith a drive chain of the bicycle to transmit the drive of the electricmotor thereto; and a torque sensor having a base mounted in fixedrelation to the frame and/or the electric motor, the torque sensorhaving a flexible arm extending from the base and a sensing membermounted to an extremity of the flexible arm, the extremity beingdisplaceable relative to the base, the sensing member being engageablewith the drive chain along a segment thereof and being displaceablethereby, the segment of the drive chain extending from the output end ofthe motor output shaft to a pedal crank of the bicycle.
 9. The electricpropulsion system according to claim 8, wherein the flexible arm of thetorque sensor is curved between the base and the extremity, a curvaturelength being defined between the base and the extremity along acurvature of the curved flexible arm, a straight line being definedbetween the base and extremity and having a straight line length, thecurvature length being greater than the straight line length.
 10. Theelectric propulsion system according to claim 8, wherein the flexiblearm of the torque sensor has a twisted portion between the base and theextremity thereof, the twisted portion having a first segment linked tothe sensing member, a second segment linked to the base, and a thirdsegment between the first and second segments, the first and secondsegments being spaced apart in overlapping arrangement.
 11. The electricpropulsion system according to claim 10, wherein each of the first,second, and third segments are curved along their respective lengths,and the twisted portion being sinuous along an extent thereof.
 12. Theelectric propulsion system according to claim 8, wherein the torquesensor is disposed within the housing.
 13. The electric propulsionsystem according to claim 8, further comprising a magnet mounted to theflexible arm between opposed extremities thereof, and a Hall effectsensor mounted to the housing and spaced from the magnet.
 14. A torquesensor mountable to a bicycle having a frame and an electric motor, thetorque sensor comprising: a flexible arm and a sensing member mounted toan extremity of the arm, the sensing member being engageable with adrive chain of the bicycle along a segment thereof and beingdisplaceable by the drive chain, the segment of the drive chainextending from an output of the electric motor to a pedal crank of thebicycle.
 15. The torque sensor according to claim 14, wherein a firstextremity of the flexible arm includes a mounting bracket and thesensing member is disposed at a second extremity of the arm.
 16. Thetorque sensor according to claim 15, wherein the sensing member includesa rotatable gear disposed at the second extremity of the arm andengageable with the drive chain.
 17. The torque sensor according toclaim 15, wherein the flexible arm is curved between the first andsecond extremities, a curvature length being defined between the firstand second extremities along a curvature of the curved flexible arm, astraight line being defined between the first and second extremities andhaving a straight line length, the curvature length being greater thanthe straight line length.
 18. The torque sensor according to claim 14,wherein the flexible arm has a twisted portion between the first andsecond extremities thereof, the twisted portion having a first segmentlinked to the sensing member, a second segment linked to the mountingbracket, and a third segment between the first and second segments, thefirst and second segments being spaced apart in overlapping arrangement.19. The torque sensor according to claim 14, wherein the flexible armhas a twisted portion between the first and the second extremitiesthereof, the twisted portion having a first segment linked to thesensing member, a second segment linked to the mounting bracket, and athird segment between the first and second segments, each of the first,second, and third segments being curved along their length, and thetwisted portion being sinuous along an extent thereof.
 20. The torquesensor according to claim 14, further comprising a magnet mounted to thearm between opposed extremities thereof.
 21. A method for converting anon-electric bicycle into an electric bicycle, the method comprising:providing an electric motor having a motor output shaft defining anoutput end, and providing a torque sensor having a flexible arm and arotatable sensing member mounted to an extremity of the arm; mountingthe electric motor to a frame of the non-electric bicycle; and extendinga drive chain at least between a pedal crank of the non-electricbicycle, the output end of the motor output shaft, and the sensingmember of the torque arm, the sensing member engaging the drive chainbetween the output end and the pedal crank.